1.0 Field Of The Invention
This invention relates generally to reciprocating diaphragm pumps, and more particularly to the sealing of the dosing piston/cylinder unit of a reciprocating diaphragm pump.
2.0 Discussion Of Related Art
The dosing precision of reciprocating diaphragm pumps depends on the exactness with which the dosing piston is sealed in the associated cylinder unit. The use of mechanical sealing elements, for example O-rings, has the disadvantage that when the sealing elements wear, dosing accuracy is reduced. In addition, it is often very difficult and expensive to maintain the narrow tolerances essential for adequate precision at the assembly stage.
European patent EP-B-0 129 187 describes a reciprocating diaphragm pump with pre-delivery. In this pump, the dosing piston is actuated via a slidably mounted drive piston. The product to be delivered or dosed is fed to the dosing piston by means of a membrane. The dosing piston/cylinder unit sealed by O-rings as the sealing element. The system of dosing piston, sealing elements and stroke adjustment screw is subject to wear and limits the useful life. The more stringent the requirements which dosing precision has to satisfy, the shorter the time a system such as this can be used without readjustment or replacement of the sealing elements.